Adds support for http.route based name

Currently http middlewares use the http method for naming spans. This solution is a not so bad low cardinality option, however from user perspective this could be improved by using the path instead of the verb. For that we can override the span name in the onPreResponse (see this in hapi for example) event so instead of having get as span name we get get /user/{user_id}.

• express
• koa
• hapi
• connect
• restify

Ping @fbaiodias @adriancole